Question

我有一个功能检查是否有可用的网络连接，我注意到它已经崩溃了一些用户。这是功能：

public static boolean isOnline() {
    ConnectivityManager connectionManager = (ConnectivityManager) RouteForMeApplication.getInstance()
            .getSystemService(Context.CONNECTIVITY_SERVICE);
    if (connectionManager == null) return false;
    boolean networkAvailable = connectionManager.getActiveNetworkInfo() != null
            && connectionManager.getActiveNetworkInfo().isConnected();
    return networkAvailable;
}

我得到的错误：

java.lang.NullPointerException
   at com.route4me.routeoptimizer.utils.InternetUtils.isOnline(InternetUtils.java:14)
   at com.route4me.routeoptimizer.services.notes.SendNoteServiceDeferred.sendNote(SendNoteServiceDeferred.java:57)
   at com.route4me.routeoptimizer.services.notes.SendNoteServiceDeferred.performAction(SendNoteServiceDeferred.java:28)
   at com.route4me.routeoptimizer.services.AbstractService$2.run(AbstractService.java:75)
   at java.lang.Thread.run(Thread.java:841)

我不明白为什么即使我检查getActiveNetworkInfo（）是否为null，它仍然会返回null。有什么想法吗？

EDIT1 错误出现在＆＃34;＆amp;＆amp; 。connectionManager.getActiveNetworkInfo（）isConnected（）;＆＃34;

Answer 1

很容易成为竞争条件。假设如果connectionManager.getActiveNetworkInfo() != null为真，那么在一纳秒后它将再次成立是不安全的。

像这样改写：

public static boolean isOnline() {
    ConnectivityManager connectionManager = (ConnectivityManager) RouteForMeApplication.getInstance()
            .getSystemService(Context.CONNECTIVITY_SERVICE);
    if (connectionManager == null) {
        return false;
    }
    NetworkInfo networkInfo = connectionManager.getActiveNetworkInfo()
    if (networkInfo == null) {
        return false;
    }
    return networkInfo.isConnected();
}

Answer 2

要访问连接管理器，您需要在清单文件中添加权限

<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"></uses-permission>

Answer 3

private boolean CheckNetWorkState() {
        final ConnectivityManager conMgr = (ConnectivityManager) mContext.getSystemService(Context.CONNECTIVITY_SERVICE);
        if (conMgr == null)
            return false;

        NetworkInfo activeNetwork = conMgr.getActiveNetworkInfo();
        return activeNetwork != null && activeNetwork.isConnected();
    }

ConnectivityManager getActiveNetworkInfo（）返回null

3 个答案: